The field of the invention is locking devices for sliding doors.
The use of sliding glass doors is widespread in our country today. Many modern apartment buildings incorporate sliding glass doors which open out onto patios and balconies. Such doors are also commonly used in houses. However, there is a major setback with these particular doors in that they are susceptible to forced entry. Most of the doors manufactured today are built with simple latch locks which can be easily popped open when a sufficient force is applied against them. Additionally, there are simple burglarly techniques which can easily open the locks. It is therefore very desirable to have available a reliable locking device which can be mounted to a sliding glass door.
A common method of locking a sliding glass door in a closed position is to prop a brace (typically a two by two piece of wood) along the sliding guide of the frame, between the slidable door panel and the stationary surrounding frame portion of the door. However, such braces are still prone to popping out of position when sufficient force is applied to the door. These braces are also somewhat inconvenient in that they must be removed and inserted every time a person wishes to unlock or lock the sliding door and this involves crouching to the floor each time to do so. This may be especially difficult for elderly people. Also, if the brace is not properly positioned (for instance, being improperly set at an angle) it can be more easily popped out of position.
U. S. Pat. No. 3,352,586 issued to Hakanson discloses a lock device for a sliding door. In Hakanson a pivotable locking member with a pull chain is mounted on the upper central portion of the door. By pulling and releasing the chain the locking member disengages and engages with teeth which are set in fixed position along the upper edge of the door frame. When the locking member is engaged, movement is prevented in either direction. There are several disadvantages with the Hakanson device. For example, the door cannot be quickly closed when the lock is engaged because the chain must first be pulled down in order to move the door. Because the locking device is in the upper central portion of the door it is clearly exposed to view and therefore tends to destroy the aesthetic effect of the sliding glass door. Also a person who wishes to move the location of the slidable door panel must reach across the width of the panel to reach the pull chain. This is an awkward maneuver to accomplish and may be particularly difficult for the elderly, especially those having an arthritic condition. Another disadvantage with the Hakansonlock is that the pull chain may be unable to be reached by small children, and would thus pose a problem to quick exit, such as when a fire occurs and the front door is unable to be used.
Other prior art, although not specifically relating to the present invention, includes: U.S. Pat. No. 4,068,872 issued to Smith which discloses a toe operated latch used for locking a cabinet door; U.S. Pat. No. 570,007 issued to Dalton which discloses a window-sash lock utilizing a ratchet shaped rack-bar secured to the window frame and a sliding lock-bolt which secures the window in a desired position; and British Pat. No. 868,209 to Newman et al disclosing a double door that incorporates a locking device within it.